As more and more medical applications are investigated and implemented to aid and assist the human body, devices needed to deliver the desired therapy are becoming increasingly more sophisticated, both functionally and in terms of their structural makeup. Modern implantable devices require power sources that are smaller in size, but powerful enough to meet the therapy requirements. For example, a cardiac defibrillator has a battery powering circuits performing such functions as, for example, the heart sensing and pacing functions. This requires electrical current of about 1 microampere to about 100 milliamperes. From time-to-time, the cardiac defibrillator may require a generally high rate, pulse discharge load component that occurs, for example, during charging of a capacitor assembly in the defibrillator for the purpose of delivering an electrical shock to the heart to treat a tachyarrhythmia, the irregular, rapid heartbeats that can be fatal if left uncorrected. This requires electrical current of about 1 ampere to about 4 amperes.
The current trend in medicine is to make cardiac defibrillators, and like implantable devices, as small and lightweight as possible without compromising their power. This, in turn, means that the components within the capacitor, particularly the anode, need to be constructed to optimum parameters as well as be free of contaminants.
Capacitor anodes typically comprise an anode active material such as tantalum, aluminum, or niobium. The anode active material is generally milled into a powdered form and pressed into a pellet. Furthermore, the anode material is generally sintered and then subjected to an anodizing or formation process before being incorporated into a capacitor. In general, the electrical performance of an electrolytic capacitor, such as energy density and leakage current, can be improved by optimally controlling the particle size, morphology, oxidation state and contamination level of the anode active material.
Current anode active material processing methods typically comprise a lengthy multi-step process that is both cumbersome and time consuming. In addition, because of the many steps, the anode active material resulting from these prior art material preparation processes is generally prone to process variability and the potential introduction of contamination which could degrade the electrical performance of the resulting capacitor.
One such prior art material preparation process is outlined in FIG. 4. This prior art anode active material preparation process consists of approximately eleven steps whereas the material preparation process of the current invention, outlined in FIG. 5, comprises only three steps. The simplified process of the present invention significantly reduces processing time and the potential for introducing contamination into the processed material. In addition, the simplified material preparation process of the present invention decreases the possibility of introducing error into the process. Furthermore, the anode material preparation process of the present invention improves material consistency, which as a result, improves the electrical performance of the capacitor.
What is needed, therefore, is a simplified, less cumbersome material preparation process that provides an anode active material with more consistent properties. In addition, what is needed is a simplified material preparation process that is less prone to processing errors and the potential of contaminating the material.